The invention relates to a master brake cylinder assembly of a motor vehicle brake system, comprising a fluid reservoir and a master brake cylinder, wherein the fluid reservoir and the master brake cylinder are fluidically coupled to each other by means of at least one fluid channel.
Such master brake cylinder assemblies are generally known from the background art. In this case the fluid reservoir is used to receive a brake fluid, which may be conveyed through the fluid channel into the master brake cylinder and from there into further regions of a fluid circuit of the motor vehicle brake system. The infeed of brake fluid from the fluid reservoir may occur temporarily in order for example to compensate wear conditions within the motor vehicle brake system. Fluid flows may occur equally as a function of individual operating states, for example in the form of a return flow of brake fluid from the fluid circuit into the fluid reservoir as a result of a reduction of a brake pressure within the motor vehicle brake system. In modern motor vehicle brake systems it is moreover a common practice for further, automatically operated brake pressure-generating devices to be connected to the fluid circuit. These may remove brake fluid from the fluid reservoir via the fluid channel and the master brake cylinder in order to build up a brake pressure.
A problem associated with such master brake cylinder assemblies is that dirt particles that are already present in the fluid reservoir prior to final assembly may mix with the brake fluid contained therein and subsequently be distributed through the entire fluid circuit of the motor vehicle brake system. In this case further components of the motor vehicle brake system that come into contact with the brake fluid may be functionally impaired or damaged. The dirt particles may equally form deposits that locally narrow or block cross-sections of flow within the fluid circuit. This impairs in particular the mode of operation of those motor vehicle brake systems which—as described above—remove brake fluid from the fluid reservoir via automatic brake pressure-generating devices. The brake fluid in these cases has to travel comparatively long distances through fluid channels of at times small dimensions within the fluid circuit, which travel may be considerably hampered by corresponding deposits. And so, as a result of an introduction of dirt particles or impurities the response behaviour of the entire motor vehicle brake system may be adversely affected.
To avoid such problems, when the fluid reservoir is filled for the first time with brake fluid or topped up during servicing, occasionally use is made of sieve arrangements that are arranged temporarily or permanently in filling openings of the fluid reservoir. These sieve arrangements prevent an ingress from the environment of dirt particles that might be dispersed from the fluid reservoir in the fluid circuit.
Such solutions cannot however prevent dirt particles or impurities, which have already been introduced into the fluid reservoir during manufacture of the master brake cylinder assembly, from mixing with a brake fluid contained therein. To combat this risk, up till now complicated processes for cleaning the fluid reservoir prior to a mounting on the master brake cylinder have been carried out. This entails separate production steps and—facilities and increases the necessary manufacturing time and the costs considerably. Also, in the event of subsequent storage or transportation of prefabricated fluid reservoirs prior to a mounting on a master brake cylinder, suitable precautions have to be taken to avoid a re-contamination of the fluid reservoir. In other words, up till now by means of relatively complicated additional measures it has been necessary to ensure that the fluid reservoir prior to mounting on the master brake cylinder is completely free of impurities.
From the background art moreover the document WO 2011/006784 A1 is known, which discloses an arrangement for preventing air bubbles from passing from a fluid reservoir into a master brake cylinder of a manually operated motor cycle brake. For this purpose, a large connecting piece that projects into the interior of the fluid reservoir is provided, which is designed with blocks that have through-openings. These are dimensioned in accordance with an anticipated size of the air bubbles. In this case too, an onward transport of dirt particles that are present in, or have been introduced subsequently into, the fluid reservoir cannot be prevented and the fluid reservoir would have to undergo a complicated cleaning process prior to mounting.
The document DE 10 2007 037 225 A1 further discloses a fluid reservoir having a filling filter that is arranged in the region of a filler neck of the fluid reservoir. As discussed above, with such an arrangement only the introduction of dirt particles during a filling operation may be prevented, whereas impurities already present in the fluid reservoir cannot be collected.
From the U.S. Pat. No. 7,261,123 B2 a reservoir container for a servo control system of a motor vehicle is known, in which a filter element is arranged between an upper and a lower housing region. The filter element is a component part of a solution to prevent the formation of air bubbles in the reservoir container.
The U.S. Pat. No. 7,261,382 B2 discloses a solution to prevent brake fluid from spraying out of the inlet opening of a reservoir container, for example during a venting of the fluid circuit through repeated actuation of the brake pedal. In this case also, a filter element may be arranged inside the reservoir container, through which filter element the brake fluid passes as it flows between various fluid chambers inside the reservoir container. During a flow out of the fluid chambers into the master brake cylinder, however, no filtering takes place, with the result that in particular production-related impurities may be dispersed substantially unimpeded in the fluid circuit.
From the U.S. Pat. No. 4,062,774 A a filter apparatus in the form of a separate assembly group is known, which may be connected by tubes to a fluid reservoir and a master brake cylinder.
It is therefore desirable to provide a master brake cylinder assembly that may be manufactured with a low outlay and at low cost.
This is achieved by various embodiments of a master brake cylinder assembly of the type described in the introduction, in which it is provided that at least one filter element is arranged within the master brake cylinder assembly in such a way that a brake fluid volume exchanged between master brake cylinder and fluid reservoir during operation flows through the filter element, wherein the filter element is designed to collect dirt particles present in the brake fluid.